The invention relates to electrohydraulic control systems of the type comprised of a way valve the valve member of which, usually a sliding spool, can be moved in dependence upon the electrical input signal applied to an electrofluidic transducer used as a pilot stage.
More particularly, the invention relates to such electrohydraulic control systems as are provided with transducers for sensing the position of the sliding spool and the load-dependent pressure at the consumer outlet of the valve, the transducers generating corresponding feedback signals which are then used in the formation of the electrical input signal applied to the pilot-stage electrofluidic transducer.
A known control system of this general type is provided with an electrofluidic transducer as a pilot stage for the way valve and its operation is modified by feedback formation. Specifically, a mechanical extension of the sliding spool of the way valve acts upon a one-armed lever which in turn, through the intermediary of a spring, acts upon the deflection-plate lever of the electrofluidic transducer of the pilot stage. Additionally, pressure gauges are arranged on a two-armed lever so that the load pressures likewise can exert an influence upon the position of the deflection-plate lever of the pilot-stage transducer, specifically through the intermediary of the just-mentioned two-armed lever and a further spring. This load-pressure-dependent feedback is intended to increase the stability of the control system, especially against consumer pressure fluctuations. However, it is extremely difficult, virtually impossible, to achieve a reliable and complete enough load-fluctuation compensation. Additionally, these purely mechanical feedback mechanisms are particularly expensive to build; they necessarily exhibit a sluggish response, and furthermore require special matching of the way valve and the pilot stage to the dimensions and movements performed by the components of the feedback mechanism, or vice versa if the feedback mechanism must be provided for a certain control valve construction, so that in general use cannot be made of widely available ready-made components.